As information communication technology has greatly developed and information communication networks have spread, electronic document based electronic transaction such as Internet shopping, banking, auction, stocks, business-to-business electronic commerce and governmental affairs have also increased. However, the electronic transactions are executed on the networks without the buyer meeting the seller, and hence, it is impossible to identify the buyer or the seller, or to check whether transacted contents are forged or altered. Also it is difficult to prevent denial of transactions.
Accordingly, techniques for using a digital signature, which has the same authority as that of a legal seal in the real world, to transmit and receive electronic documents have recently been developed, and services for verifying the relation between the owner of a digital signature and the key used for a digital signature have been provided.
In general, when a user visits a certificate register authority, is identified, and request issuance of a certificate, the certificate register authority provides the user's information to a certification authority server which provides certificates on the network and requests registration, and when the user accesses the certification authority server and requests the issuance of a certificate on the network therefrom, the certification authority issues a certificate and provides the same to the user's terminal, and the user then uses the certificate to safely execute transactions such as Internet shopping, banking, auction, and stocks on the network.
However, the user is allowed to use the certificate only through the corresponding terminal (e.g., wired or wireless terminals including a computer and a cell phone) to which the certificate is downloaded. In particular, the mobility of the certificate is further restricted when the certificate is downloaded to a wired terminal.